The invention relates to a process and an apparatus for continuously withdrawing a partial current from a current of crude gas for obtaining a specimen for the gas analysis in order to properly control and supervise the process.
In the art of gas generation, for instance during oxygen pressure gasification, hot steam saturated crude gases are obtained which are under a highly elevated pressure. These gases cannot be directly passed into a gas analysis device or an associated pressure reduction precision valve where they are necessary for the optimum control of the operation. Instead, it is necessary to subject them to a pretreatment prior to the gas analysis. This type of pretreatment is the object of the present invention.
The invention can also be used in the continuous withdrawing of specimens by means of a sound in case of natural gases which flow at a high temperature and at high pressure and are likewise steam saturated and contain solid components and hydrocarbons which are subject to condensation when the gas is cooled.
The process and apparatus of the invention can furthermore be used for devices where crude gas mixtures are passed through conduits, particularly in the chemical industry and where similar difficulties are encountered when a specimen is to be obtained for gas analysis.
It has already been known to withdraw crude gas from a gas current through a detour and then to subject the branch current to pressure release in a valve and to pass the branch current through further devices for regulating the gas pressure.
This prior art process does not enable a sufficient purging of the crude gas. It also involves risks regarding the safety of the apparatus and is not in accord with the rules in this respect since the tars and dusts from the crude gas may cause an uncontrollable pressure build up in the specimen withdrawal system. Even a subsequent purging of the gas specimen by means of ceramic filters or other filter materials does not lead to a sufficient degree of purity to assure a constant uninterrupted operation of the analysis apparatus.
Such uninterrupted operation of the analysis apparatus likewise could not be obtained by employing filters for the gas which was still under high pressure. Irrespective whether these filters consist of ceramic fibrous or porous organic materials they result after comparatively short operating times in clogging up and thus in a failure of the analysis apparatus. To eliminate the clogging up a cleaning or exchange of the filter is necessary which requires substantial amounts of time.
The use of electrofilters, particularly for separating liquid mists, for instance in case of tars and solid materials is impractical where the possibility of formation of explosive gas mixtures exists which can never be excluded in case of the oxygen pressure gasification of solid fuels.
The addition of safety devices such as flame safety valves and similar likewise results in an unacceptable increase of the expense of the apparatus.
In addition, this manner of avoiding the risk would not guarantee a perfect separation of the pollutants. The removal of the separated pollutants which may exist in several phases, such as liquid, paste-like or solid, results in further difficulties and expenses.
It has also been proposed to effect the separation of liquid and solid pollutants by means of said centrifugal separators.
This proposition has the disadvantage that under the conditions of operation emissions may appear at the inlet nozzles and at the walls of the cyclone. In view of the high pressure it is then necessary for safety reasons to carry out periodic measurements of the wall thickness at relatively short periods of time. Besides, the removal of the separate products again involves considerable difficulties. A process for the continuous withdrawal of specimens of a polluted gas at high temperatures, particularly a crude gas as obtained in a lignite pressure gasifier and an apparatus for carrying out this process has been described in the patent of the German Democratic Republic No. 94,909. In this process, however, clogging up and failure of the analysis apparatus occurs by the lack of a reheating of the separated product prior to removal by the specimen withdrawal system, furthermore by the use of horizontal conduits and finally by the absence of an anisokinetic withdrawal of the branch current. The Patent No. 110,345 of the German Democratic Republic also describes a process and apparatus for withdrawing a gas which is charged with dust and condensate and is under pressure, particularly a crude gas for purpose of the analysis. In this case a gas current is produced in the branch by means of a baffle or shutter provided in the main conduit.
This baffle or shutter constitutes, however, a serious risk regarding the withdrawal of the products from the main conduit in case of gases which contain large proportions of dust and tar.
Extended investigation has shown that a mere one-time withdrawal of the specimen current, countercurrent to the main current, results soon in a clogging up of the specimen withdrawal system and in an interference with the gas analysis system by pollutants, particularly in those cases where a forced circulation in the branch circuit is not provided.
In this area of technology it has also become known that it is possible to reintroduce parts of the branch current into the main current by means of a pump, for instance a steam jet or injector. If the pump is provided at the outer terminal of the specimen withdrawal system, the gas composition within the system will not be affected.
It has also become known that the products separated out in the crude gas current can be reintroduced continuously by means of such pump into the initial gasification system.
It is an object of the present invention to provide for a process and apparatus by which in case of a highly polluted crude gas and upon observance of all safety regulations, a cold gas specimen can be passed into the gas analysis apparatus in a continuous operation and practically without requiring any special service and at a minimum idling time. This specimen gas should then be free of pollutions and its basic composition should not be modified by the process of withdrawal from the main gas current.